Apparatus for coating steel tubes.

The invention is directed to an apparatus for coating of steel pipes with plastic according to the preamble of claim 1.

It is known to coat steel pipes with a thermoplastic resin layer by being passed in a heated state by the trained than ring die slit of an extruder head and are thereby coated with a film tube which is connected by means of an adhesive to the pipe surface (eg DE-PS 22 22 911 or DE-OS 17 04 851) For pipes of larger diameter, it is known to produce the casing by helically wrapping a strip-shaped thermoplastic film, wherein the tubes set in rotation and passes in the longitudinal direction at a designed as a slot die, slot die of an extruder head (eg DE-PS 17 71 764 or DE-PS 19 33 206). Also in this case, the connection of the plastic layer with the tube surface is carried out by gluing with a contact adhesive.

With the DE-PS 15 54 776 it has become known for the wrapping with a tubular film to assign the ring die, a vacuum chamber, which is connected to a vacuum pump which creates a vacuum between the tube surface and exiting from the annular slit tubular film. This regulation is intended that the tube closely abuts against the tube. As a seal against the negative pressure generated within the nozzle is a cuff, which is arranged on the pipe inlet side of the extruder head and the uncoated tube closely surrounds.

The permitted height of the negative pressure and thus the anpressende effect of the external air pressure are limited by the low mechanical resistance of the spanned between the extruder die and the tube to be coated warm thermoplastic film. The sealing of the vacuum chamber by a collar made of soft, elastic material may blasted excessive wear the cuff on with steel grit and thus rough pipe surface. In addition, the abrasion of the cuff may affect the adhesion of the coating on the pipe. The use of metallic sealing elements can inversely affect the blasted pipe surface.

Particular difficulties arise when pipes are to be coated, which are provided in an immediately preceding step with a primer (eg, epoxy resin), which is viscous or mechanically easily damaged even at the processing temperature.

These known methods have in common that the tubes are passed through a cooling path following the jacket so that the still warm plastic layer is quickly cooled to room temperature. For this purpose it is known to form on the coated tubes a film of water by sprinkling with cooling water of low pressure. This may be the case that splashing incident on the still soft thermoplastic layer when the freshly coated tube leaves the coating station (ring die or slot die). Since this layer is still very sensitive to pressure, column, water droplets can leave undesirable scars that remain even after cooling.

The invention proceeds from DE-OS 17 29 309, which has a pressure device for the plastic coating between the extruder head and the cooling section. This apparatus may be embodied as a pressure jaw, but it is also proposed to produce the pressure on the plastic material from escaping from the nozzle water. The mechanical pressure device can cause damage to the shell surface, while by the pressure of water spray effect occurs, which may cause the aforementioned disadvantages.

The object of the invention is therefore, the above-mentioned device such that both a pressing of the plastic is possible as well as the impact of splashing can be avoided in sensitive parts of the still fresh coating. This object is achieved according to the invention having the features indicated in claim. 1

Preferably further developments result from the dependent claims.

The invention is based on the idea to include the freshly coated steel pipe with a mechanical seal, which consists essentially of an annular elastic-soft foam body with at least partially open pores. Through the pores of the Schaumstoffkröpers tubecover is a cooling liquid, such as water supplied. A uniform action of the coolant is achieved in the fresh shell; on the shell forms a cooling and simultaneously lubricating liquid film. The use of such seals makes it possible to effectively close off any areas of the coated steel pipe from the environment.

In development of the invention it is proposed to arrange the foam body of the mechanical seal in an annular sheet metal container to which the supply lines are connected to the cooling liquid. In order to facilitate the threading of a steel pipe in the mechanical seal, the ring opening of the foam body is not formed on the provided for the pipe inlet side cylindrical advantageous funnel-shaped as in the space provided for the tube exit side. It is also advantageous to assemble the foam body of the mechanical seal of several sections that are pressed together firmly in the operating state. It is also advisable to assemble the foam body consists of two half-rings and the metal containers in accordance of two hinged halves. Moreover, the two casing halves may be sealed off in the plane of division by housing walls against each other and connected to each one separately controllable supply for the cooling liquid. For example, by controlling the Mühlmittelmenge in the leads compensate for the otherwise through the different hydrostatic pressures (when large-diameter pipes, the pressure difference may be up to etwa.2 m WS.) induced different quantities of coolant on the lower and upper half of the surface of the coated steel pipe obtained will. The purpose of the coolant flow control, it also serves to form the foam body with a decreasing from below upward flow resistance. The flow resistance can be achieved by for example a different pore structure of the S_chaumstoffkörpers vary in vertical direction. On the other hand it can also be influenced by the fact that parts of the surface of the ring opening of the foam body with a dense coating, for example of silicone rubber, are provided.

To demonstrate the effectiveness of the mechanical seal in the case of a displacement of the tube axis, to ensure, for example, due to vibration during transportation of the steel tubes, at any time in development of the invention it is proposed to mount the mechanical seal of an elastically flexible holding device. Further, it is possible to construct due to the isolation effect of the mechanical seals, various cooling zones having different cooling conditions, in which a plurality of mechanical seals apart are arranged axially one behind the other along the coated tube.

Finally, in an advantageous development of the invention proposes to use the mechanical seal to seal an overpressure chamber, which is used instead of the described vacuum chamber. The hyperbaric chamber joins with its substantially cylindrical housing directly to the ring die of the extruder head, so that the tube exit side of the extruder head and the pipe inlet side of the overpressure Kamer are sealed to each other. On the pipe inlet side of the pressure chamber, the introduced pressure is sealed by the inner surface of the extruder head and the outer surface of the still soft thermoplastic tubular film, while the required sealing effect is achieved on the tube exit side of the overpressure chamber through an arranged there, and with the housing of the pressure chamber closely attached mechanical seal. By this arrangement it is achieved that the thermoplastic tubing is pressed in a similar manner by the action of a negative pressure chamber on the tube, without the disadvantages of a vacuum sealing cuff described must be taken into account. The sustainability of warm thermoplastic tubular film which is clamped between the steel tube and the extrusion die, limited place in the same manner as in the vacuum chamber, the permissible pressure difference between the inner and outer surface of the tubular film. As advantage arises that is further enhanced by the elastic pressing of the lubricated with the cooling liquid foam body of the mechanical seal and the seals, as far behind the hyperbaric chamber to form insular cooling zones are still more mechanical seals arranged, the effect of pressing the coat film on the steel pipe.

The invention is explained below with reference to embodiments illustrated schematically in the drawings.

Show it:<ul><li>Fig. 1 A mechanical seal in a tube coating system,</li><li>FIG. 2 is a mechanical seal in a winding wrapping machine,</li><li>Fig. 3 a section through a mechanical seal,</li><li>Fig. 4 is a front view of a split mechanical seal,</li><li>Fig. 5 is a front view of a split mechanical seal in the non-assembled state,</li><li>Fig. 6 is a rear view of the mechanical seal shown in Fig. 5 in the assembled state,</li><li>Fig. 7 shows an arrangement of multiple seals to form insular cooling zones,</li><li>Fig. 8 is a shock-mounted mechanical seal in front and side view,</li><li>FIG. 9 is a section through an extruder head with ring die and connected hyperbaric chamber.</li></ul>

Similar parts are designated in the drawings with the same reference characters.

Fig. 1 shows schematically the use of the mechanical seal according to the invention in the steel pipe coating by the tube extrusion process. The preheated steel tube 10 is passed through the extruder head with annular slot 1 and sheathed with the tubular plastic film 11 (for example polyethylene).

In the production direction behind the extruder head, the mechanical seal according to the invention consisting of the housing 4 and the therein foam body 3 is disposed. The feed line for the cooling medium is not shown. The foam body 3 comprises the coated steel tube 10 and is dense with formation of a lubricating film through the cooling liquid on the surface of the coat film 11. Thus, the mechanical seal shields lying between the mechanical seal and the extruder head 1 part of the sheathed steel pipe 10 from the influence of spray from the seen in the production direction arranged behind the mechanical seal, cooling section, not shown here.

Fig. 2 shows one of the Fi. appropriate arrangement of the mechanical seal in a plant for the coating of steel pipes by the filament winding process. 1 Here, a shallow winding sheet 11 extruded from a slot die 2 of an extruder head. The associated extruder is again not depicted. The steel pipe 10 is helically guided past the slot die of the extruder head 2 and wrapped with the extruded film eleventh Which is arranged downstream of the extruder head comprises mechanical seal in the same manner as in the first example, the umhUllte steel pipe 10 and in turn causes a partitioning of the downstream cooling path, which is not shown here in detail.

The sectional view in Fig. 3 shows the structure of the mechanical seal in detail. You bsteht initially from an example made of sheet metal housing 4 with a cylindrical casing. The mutually facing surfaces 10 have corresponding circular openings for the implementation of the coated steel pipes. For the supply of the cooling liquid, a supply line 5 is provided on the surface of the housing. 4

The ring-shaped foam body 3 is arranged concentrically in the cylindrical housing 4th The foam body 3 also has f + r the implementation of the clad steel pipes 10 has an opening having a substantially cylindrical surface 7b. For ease of threading the steel tubes 10, the surface 7a of the opening of the mechanical seal on the pipe inlet side formed advantageously in a funnel shape. From the drawing is further seen that a distributing chamber 8 is arranged for the cooling fluid on the inside of the casing 4 between the cylinder sheath and the outer surface of the foam body. 3 The air flowing through the feed line 5 can thus cooling liquid the foam body umgebea 3 over its entire circumference. The foam body 3 has an open pore structure. Thus, the pressurized coolant can flow through the foam body 3 and at the surface 7a, 7b, which rests on the clad steel pipe 10 emerge. In this way, a uniform coolant film is formed on the surface of the tube sheet 11 is formed, which causes a lubricating effect and thereby prevent the pressure applied with a mechanical pressure on the tube sheet 11 foam body 3 is damaged, the surface of the pipe encasement eleventh The pressure action of the foam body 3 supports the applying desired density of the tube sheet 11 to the surface of the steel pipe 10th

Fig. 4 shows a front view of a mechanical seal, which is made in development of the invention with a split housing 4a, 4b. The lower casing half 4b is connected to the inlet 5, the upper casing half 4a at an outlet 14 for the cooling liquid. The foam bodies 3a, 3b, as the housing 4a, 4b is divided into two halves and together with the housing 4a, 4b hinged executed. In an advantageous embodiment of the invention is the lower half of the foam body 3b for example by designing the pore structure or by applying a barrier coating on parts of the surface 7a, 7b of the opening for the pipe penetration with a greater flow resistance formed for the cooling liquid than the upper half of the foam body 3a.

Thereby a compensation for the otherwise caused by the different amounts of the different hydrostatic pressure on the upper or lower half of the tube sheet exiting cooling liquid and the related cooling effect is achieved. As the pressure difference increases with the diameter of the steel to be coated tubes 10, is the version with varying flow resistance in the parts of the foam body 3a, 3b recommended particularly in the sheathing of large pipes. This effect can be achieved illustrated constructive measures by the in FIG. 5 and 6 in the front and rear view of a mechanical seal. Here again, the housing 4c, 4d and the foam body 3c, 3d running in two separate halves. Both housing halves 4c, 4d each have a separately controllable supply line 5a, 5b for the cooling medium. In contrast to FIG. 4, the housing halves 4c, 4d completed in the parting plane up to a portion which is filled by the foam body 3c, 3d, through housing walls 6. Thus, the distribution space for the coolant is in contrast to FIG. 4, where the distribution chamber 8a, 8b forms a self-contained space, divided into two completely separate areas 8c, 8d. By controlling the coolant flow through the supply lines 5a, 5b, equal amounts of the exiting cooling liquid can spite of the same pore structure of the foam body 3c, 3d in the two halves of the mechanical seal can be set.

Fig. 7 shows three in a cooling line axially successively arranged seals, by the contra-insular cooling zones .Between the seals are formed. By in each cooling zone individually adjustable amount of cooling liquid, which is symbolized by the drawn, downward arrows, different cooling conditions can be realized. To avoid negative consequences caused by displacement of the tube axis, as a result of vibrations caused by the transport means of the pipe coating plant, the mechanical seal is provided with a resiliently movable suspension. In Fig. 8 this suspension is realized by two weight-loaded cables 9a and 9b, two coil springs.

A further advantageous embodiment of the invention is shown in FIG. 9; Here, the steel pipe 10 is provided in a ring die with the plastic sheathing 11th In order to improve a tight application of the plastic jacket 11 on the surface of the steel pipe 10, a pressure chamber is arranged with a substantially zyliderförmigen housing 12 behind the annular slot 1 of the extruder head, which can be filled through the feed line 13 with compressed air. While the overpressure chamber 12, 13 is sealed on the extruder head side by the extruded tubular film 11 and the surface of the annular slot 1, the required seal on the tube exit side of the overpressure chamber through the inventive mechanical seal with the housing 4, the coolant supply 5 and the foam body 3 realized. This arrangement ensures that the splashing of the subsequent cooling zone, not shown, can not penetrate into the freshly coated areas of the steel pipe 10 and that the overpressure chamber 12, l3 well sealed without going through the necessary, the surface of the tube sheet 11 contact sealing element damage to the tube sheet 11 elicit. Incidentally, 11 receive funding of by the mechanical pressing of the tube sheet 11 to the steel pipe 10 through the steel pipe 10 enclosing foam body 3, the tight contact of the pipe encasement of the steel pipe 10th